Vision and Central Visual Pathways Flashcards
Describe the pathway of the Optic Tract
Eye–> Optic Nerves (CN2) –> Optic Chiasm–> Optic Tract–> Hypothalamus, Lateral Geniculate Nucleus, Superior Colliculus, Striate Cortex
Describe the vision and eye placement of prey animals.
Laterally placed eyes
Increased peripheral vision to see predators coming
Monocular vision- bad depth perception
Which type of animal has more decussation? Predator or prey animals?
Prey animals have more decussation
What 4 pathways do Optical nerves take after penetrating the optic disk?
The Retino-_____ pathways!
- Geniculostriate
- Pretectal
- Tectal
- Hypothalamic
Which retinal pathway(s) are cortical?
Only the retinoGeniculostriate pathway
Which retinal pathway(s) are non-cortical?
The rest: Pretectal, Tectal, and Hypothalamic
Which pathway travels via the Lateral Geniculate Nucleus?
Retinogeniculostriate
Which pathway travels via the Pretectal nuclei?
Retinopretectal
Which pathway travels via the rostral/superior colliculi?
RetinoTECTAL
Which pathway travels via the suprachiasmatic nucleus?
RetinoHYPOTHALAMIC
Which pathway is associated with:
conscious perception of vision
Menace Response Pathway
Retinogeniculostriate
Which pathway is associated with:
PLR (pupillary light reflex)
RetinoPREtectal
Which pathway is associated with:
Ocular Fixation Reflex
RetinoTECTAL
Which pathway is associated with:
Circadian Rhythms
RetinoHYPOTHALAMIC
What % of optic tract axons go to the LGN in the Thalamus?
80%
What tests do we use to test for conscious perception of vision (Retinogeniculate Reflex)?
Maze
Cotton Ball
Visual Placement Test: Animal attempts to place paws on table in front of them
Menace Response
What % of axons bypass the LGN and synapse onto the Pretectum or Rostral Colliculus?
20%
What is the Edinger-Westphal Nucleus?
The parasympathetic nucleus of CN3
Associated with RetinoPREtectal Pathway
Axons synapse here after synapsing onto the pretectum and rostral colliculus
What is the result of axons synapsing onto the Edinger-Westphal Nucleus?
Pupil constriction
What is Miosis? Which pathway is it associated with?
Pupil constriction- RetinoPREtectal Pathway
How do we use a penlight, pupillary light reflex (PLRon) and the RetinoPREtectal Pathway to test for lesions?
You are testing Sensory of CN2 and Motor of CN3
Do a direct test of PLR and an indirect test of PLR on both eyes- OS- left and OD- right
What is O.S.?
Left Eye
What is O.D.?
Right Eye
Where is the lesion located if you get negative PLRs for both direct and indirect tests of the O.S. (left eye), but positive PLRs for the O.D. (right eye)?
Lesion of the optic nerves BEFORE the optic chiasm associated with Sensory CN2
If you have a lesion ON the optic chiasm, what would your direct and indirect PLR tests look like?
For O.S. (left eye): Direct and Indirect PLRs both +
For O.D. (right eye): Direct and Indirect PLRs both +
If there is a lesion located AFTER the optic chiasm on the RIGHT side, what would your direct and indirect PLR tests look like?
For O.S. (left): Direct and Indirect PLRs both +
For O.D. (right): Direct and Indirect PLRs both +
Where could there be a lesion if direct and direct PLR tests of both right and left eyes come up (+)?
AT the optic chiasm or after the optic chiasm
What is a common problem seen with brainstem trauma?
PLR abnormalities
What is Anisocoria?
Uneven pupil size
What is the retinoTECTAL pathway for?
For reflex movements of the eyes and head towards visually interesting stimuli and processing visual info withOUT conscious awareness.
What is “blindsight”
The processing of visual info without conscious awareness
Describe the pathway of axons of the retinoTECTAL pathway.
Axons–> Rostral Colliculi (in the midbrain)–> MANY PLACES!
CN-3,4,6
Spinal Muscles
Thalamus
Cerebellum
The RetinoHYPOTHALAMIC Pathway is especially important in what species?
Sheep and Goats, and HORSES
for reproductive cycles associated with circadian rhythms and photoperiods
If there is a loss of PLR…
How can you tell if the problem is due to a CN2 deficit or a CN3 deficit?
Using the INDIRECT test!
If problem in CN2, NEITHER eye has PLR.
If CN3 isn’t working, ONLY the affected eye has no PLR (either direct or indirect).
Where in the Vision Pathway would you see partial decussation?
Between the optic chiasm and optic tract AND
Between the Pretectal Nuclei and the EWN
If I say “STARTLE REFLEX” you say:
TECTAL pathway!
What is Horner’s Syndrome?
Lose innervation to the eye and 3rd eyelid comes up
Due to:
Preganglionic= Disc rupture, neck trauma
Postganglionic= Otitis or Orbital Disease
HAPPENS RANDOMLY- Most common- Idiopathic mean random
